1. Indices of Road Erosion Bear Valley Watershed, Idaho
CEE 6440: GIS in Water Resources
Nov. 30, 2010
Jeanny Wang Miles

2. Measuring Road Erosion Risk
Fine Sediment from Unsealed Roads harm downstream ecosystems (suffocate redds)
Roads Need Adequate Drainage & Maintenance
Inadequate Culverts Impede Fish Passage
Difficult to Assess Actual Impact from Roads
Good Models Need Good Field Data
Image Analysis to Help Prioritize Erosion Risk on Watershed Scale?

3. Primary Questions
How and where does the road system modify surface and subsurface hydrology?
How and where does the road system cause surface erosion?
How and where is the road system hydrologically connected to stream system?
How and where does the road system cause mass wasting?

4. Indicators of Road Hazard
Road Density (< 1, 1-2.5, > 2.5 mi/mi2)
Stream Channel Proximity (300 ft from stream)
Predicted Stream Crossings
Slope Class (within 10 percent gradients)
Mass wasting: Bedrock geology or geomorphology as indicators of road erosion hazard (unstable surfaces)
Not used in this analysis
Slope Position as an indicator of road hazard (upper 20%, middle 40%, lower 40%)
Maintenance: Best management practices as indicators of road hazard

5. Bear Valley Watershed, Idaho
- Listed as 303(d) impaired for sediment under Clean Water Act
- 191 square miles in watershed
>148 miles of roads

6. Bear Valley Creek and Elk Creek
Subwatersheds
Includes two 5th HUC watersheds:
Bear Valley Creek and Elk Creek
Includes seven 6th HUC subwatersheds

7. Road Density 0.88 mi/mi2 0.46 mi/mi2 Good : < 1 mi/mi2
Fair: mi/mi2
Poor: > 2.5 mi2
1.5 mi/mi2
0.27 mi/mi2
HUC_12
HU_6_NAME
Road (mi)
SqMi
Density
Upper Bear Valley
49.00
26.28
1.86
Bearskin
26.33
17.58
1.50
Lower Elk
18.27
20.79
0.88
Cache
34.37
39.97
0.86
Wyoming
11.95
25.74
0.46
Fir Creek
5.51
20.18
0.27
Upper Elk
2.85
40.81
0.07
TOTAL
Bear Valley Watershed
148.27
191.34
0.77
0.86
mi/mi2
1.86 mi/mi2

8. Stream Channel Proximity
Roads within
300 feet stream buffer
Good : <10% roads within buffer
Fair: 10-20% roads within buffer
Poor: >20% roads within buffer
Subwatershed m
mi in Buffer
total mi
% rds
Fir Creek
6930.6
4.3
5.1
79%
Bearskin
14.3
14.9
56%
Wyoming
9385.1
5.8
6.3
51%
Cache
14.5
43%
Upper Bear Valley
16.9
17.2
35%
Lower Elk
8597.2
5.3
5.6
30%
Upper Elk
956.7
0.6
0.9
28%

9. Stream Crossings Good : < 0.2 X-ings/stream mi
Fair: 0.2 – 0.4 X-ings/str mi
Poor: > 0.4 X-ings/stream mi
StreamCross - intersect of roads & DEQ streams layers
180 StreamNetCross – intersect of roads & TauDEM flownet
176 STRM_CRO observations
191 inventoried from GRAIP
HU_6_NAME
Stream Density
Stream Crossings
Stream Miles
# Cross/
Str Mi
Upper Bear Valley
1.2
19.0
31.5
0.60
Bearskin
1.4
14.0
25.5
0.55
Cache
13.0
49.1
0.26
Wyoming
1.5
7.0
38.6
0.18
Fir Creek
4.0
23.4
0.17
Lower Elk
1.6
3.0
33.0
0.09
Upper Elk
1.3
1.0
51.7
0.02
TOTAL (average) 61
252.8
0.24

10. Slope at Drainpoints - Broad Based Dips
Slope Class
Slope at Drainpoints - Broad Based Dips

11. Mass Wasting (LandTypes)
Percent of roads network
within “unstable” landtypes.
C1: Fluvial lands with moderate to high mass wasting potential C1 C2 D1 D2 F1 F5 G1 G2
Upper Elk
31%
19%
15%
Wyoming 7% 3%
63%
12%
0.4%
Fir Creek
19.4%
1.95%
4.5%
74 %
Lower Elk
1.2%
0.3%
2.1%
26.8%
Bearskin
24.7%
12.9%
10.5%
1 %
1.0%
Cache
17.3%
19.6%
47.1%
0.2%
2.6%
Upper Bear Valley
19.0%
49.9%
0.7%
20.0%
2.7%

12. Geomorphic Road Assessment and Inventory Package (GRAIP)
- process and tools for analyzing road erosion
- combines road inventory with GIS analysis
- predicts road sediment production & delivery, mass wasting risk from gullies and landslides, and road hydrologic connectivity
- overlays road path on Digital Elevation Model (DEM) and uses TauDEM for flow accumulation
Sediment production for each road segment:
E = B x L x S x R x V
(base rate, length, slope, surface, vegetation)

13. GRAIP Sediment Accumulation
Percent SedDel / SedProd %
Fir Creek
20.4%
Upper Bear Valley
12.6%
Bearskin
11.2%
Wyoming
8.1%
Cache
7.5%
Lower Elk
4.4%
Upper Elk
2.0%

14. GRAIP Sediment Delivery
Percent SedDel / SedProd %
Fir Creek
20.4%
Upper Bear Valley
12.6%
Bearskin
11.2%
Wyoming
8.1%
Cache
7.5%
Lower Elk
4.4%
Upper Elk
2.0%
Sediment Delivery (kg/yr)
sedDel
Upper Bear Valley
388,658
Bearskin
140,574
Cache
94,441
Fir Creek
58,874
Lower Elk
48,336
Wyoming
10,500
Upper Elk
3,150

15. 3. Crossings / Stream Mile
Relative Comparison
HUC_6_NAME
1. Density
2. Stream Proximity
3. Crossings / Stream Mile
Ave ranking
123 Index
sedDel (kg/yr)
% Total sedDel
Upper Bear Valley
1.86
34%
0.60
2.67
38.72%
388,658
52.2%
Bearskin
1.50
54%
0.55
44.86%
140,574
18.9%
Lower Elk
0.88
29%
0.26
2.00
6.80%
48,336
6.5%
Cache
0.86
42%
0.18
1.67
6.57%
94,441
12.7%
Wyoming
0.46
49%
0.17
3.87%
10,500
1.4%
Fir Creek
0.27
78%
0.09
1.94%
58,874
7.9%
Upper Elk
0.07
21%
0.02
0.03%
3,150
0.4%
TOTAL
0.77
44%
0.24
2.0
8.23%
744,532
100%

16. Conclusion Bear Valley Watershed Road Erosion
Upper Bear and Bearskin roads deliver most sediment to streams
Sediment Delivered (kg/yr)
sedDel
Upper Bear Valley
388,658
Bearskin
140,574
Cache
94,441
Fir Creek
58,874
Lower Elk
48,336
Wyoming
10,500
Upper Elk
3,150

17. Conclusion Image analysis can help prioritize erosion problems
Indicators confirm
GRAIP model predictions
(in a relative sense)
Sediment Delivered (kg/yr)
sedDel
Upper Bear Valley
388,658
Bearskin
140,574
Cache
94,441
Fir Creek
58,874
Lower Elk
48,336
Wyoming
10,500
Upper Elk
3,150

18. Questions?

20. Secondary Questions
How and where do road-stream crossings influence local stream channels and water quality?
How and where does the road system restrict the migration and movement of aquatic organisms?
How and where does the road system affect shading, litterfall, and riparian plant communities?
How and where does the road system contribute to fishing, poaching, or direct habitat loss for at-risk aquatic species?
How and where does road system facilitate introduction on non-native species?